1. Field of the Invention
The present invention relates to a gas laser machining apparatus, for example, a CO2 laser machining apparatus, and more particularly to a technique that enables laser piercing by a stable pulse laser.
2. Description of the Related Art
In piercing fine apertures by the CO2 laser, the pulse laser piercing conditions contain the number of pulses which determines how many laser pulses are irradiated onto each aperture location, in addition to pulse energy, pulse peak, pulse width and so on. The number of pulses irradiated on one piercing location is several pulses at the maximum although being dependent on the material, thickness, etc., of a workpiece. Therefore, one mis-pulse seriously adversely affects the piercing result.
In a conventional pulse control, a laser output shown in FIG. 9B is obtained when an input power waveform shown in FIG. 9A is applied to a laser device. As disclosed in Japanese Patent Unexamined Publication No. Sho 63-7688, when a base power is added to the power waveform as shown in FIG. 9A, the laser pulses are improved in their leading and trailings characteristics and stability. However, it is difficult to stabilize the discharging state immediately after a discharge of energy is made. As a result, it has been recognized that a pulse first generated by the laser device becomes a mis-pulse of a low peak once per four times, as shown in FIG. 9C, although infrequently. Therefore, there is a case where a lower number of pulses than the set number of pulses for other aperture locations are irradiated on a first aperture location immediately after the piercing process starts.
A process of piercing a fine aperture using laser pulses in the conventional gas laser machining device is conducted as described above, and because it is necessary to irradiate laser pulses of a set number on the respective aperture location, there is a risk that the occurrence of a mis-pulse leads to piercing failure. Therefore, it is helpful to provide the oscillation of laser pulses which is stabilized without any mis-pulse.
The present invention has been made to solve the above problems with the prior art, and therefore an object of the present invention is to provide a gas laser machining apparatus which ensures a stable pulse laser oscillation without producing mis-pulses, to thereby realize piercing of fine apertures.
To achieve the above object, according to the present invention, there is provided a gas laser machining apparatus that conducts a pulse laser oscillation, a preparatory pulse component whose energy is below a threshold value of a laser oscillation, is located prior to a first pulse of discharging pulses.
Also, according to the invention, a base power whose energy is below the threshold value of laser oscillation is added during the machining operation, and a preparatory pulse component whose energy is below the threshold value of laser oscillation is located prior to a first pulse of the discharging pulses.
Further, according to the invention, a preparatory pulse component whose energy is below the threshold value of laser oscillation is continuously applied before laser pulses used for machining are generated and in each of the intervals between the adjacent pulses used for machining.
Still further, according to the invention, a preparatory pulse component whose energy is below the threshold value of a laser oscillation is applied for a given period prior to the respective pulses used for machining.
Yet still further, according to the invention, a laser beam is scanned so that a first pulse of laser pulses is prevented from being irradiated to a workpiece.